5i8 



NATURE 



[September 24, 1908 



T 



THE ROYAL PHOTOGRAPHIC SOCIETY'S 

 ANNUAL EXHIBITION. 



HIS exhibition, which will remain open for a few 

 weeks, is, as usual, at the New Gallery, Regent 

 Street. It is divided into several sections, namely : — 

 (i) pictorial ; (2) scientific and technical ; (3) lantern-slides ; 

 (4) autochromes ; (5) portraits of eminent British subjects 

 from the society's collection; (.6) general professional work; 

 (7) trade exhibits of apparatus and materials. We notice 

 a welcome though slight tendency in the pictorial section 

 to return to the old custom of stating by what process the 

 print has been produced, information that is not only due 

 to any prospective purchaser, but also gives the exhibit an 

 interest for the technical student, while it in no sense 

 detracts from its pictorial value. 



There are no new methods of photography in colours. 

 The coloured prints in the pictorial section are, so far as 

 we notice, coloured by hand. The chief interest of the 

 autochromes lies in the application of these plates to the 

 photography of other subjects than portraits, views, and 

 still-life groups. Dr. H. G. D. Brockman demonstrates, 

 in a series of thirteen, their usefulness in recording the 

 presence of blood-stains in a room, on various articles of 

 clothing, and on a bottle, in connection with a trial for 

 murder. In some cases the article was " subjected to a 

 stream of oxygen in an atmosphere which was super- 

 saturated with water vapour and at a temperature of 

 70° F. As a consequence, certain tarry-looking stains on 

 the boots which were thought to be blood became ruddy." 

 The effect of this treatment is shown by comparative photo- 

 graphs. The same exhibitor has eight autochromes of 

 pathological subjects, which will convey a very good idea 

 of what may be expected when these plates are used for 

 suoh work. Mr. C. P. Butler shows a direct photograph 

 of the solar spectrum taken on " Uto " paper, in which 

 the colours of the spectrum are excellently rendered. 



The natural history division includes a few autochromes 

 which show the great advantage of colour photographs of 

 such subjects, in spite of the fact that the tints depend to 

 a certain extent upon the manipulation of the plates. In 

 a very considerable collection of monochrome photographs, 

 "The Stoat," by Mr. Douglas English, appears, we 

 believe, for the first time. There are several series of 

 pictures of great interest. Mr. William Farren, for 

 example, gives fourteen photographs of the nest of a song 

 thrush, which illustrate the rapid growth of the young 

 birds and the feeding of them by the parents, and he 

 appends a short history of the events, with dates and many 

 details, from the hatching to the time the nestlings left 

 the nest. Similar series are contributed by Mr. Alfred 

 Taylor, which illustrate the " domestic habits of the song 

 thrush" and "the life-history of the tawny owl." A 

 series of eight radiographs, by Messrs. Wilson and 

 Blackall, show the gradual development of the bones of 

 the hand from three to eighteen years of age. Among 

 the photomicrographs, some examples of low-power work, 

 of five and ten diameters, by Mr. W. F. Cooper, are 

 specially noteworthy. 



The progress made in cutting the Panama Canal is 

 clearly shown in ten photographs by Dr. Vaughan Cornish, 

 with a map and vertical section. Mr. J. Howden Wilkie 

 has succeeded in two cases in photographing the same 

 flash of lightning with both a stationary and a moving 

 camera. Captain Owen Wheeler, who has made a 

 speciality of telephotography, demonstrates in a remark- 

 able way that it is possible to produce telephotographs of 

 seven and nine diameters' magnification of such good 

 definition that they will well stand a further enlargement 

 of four diameters. The detection of forgery by photo- 

 graphic means is well illustrated by Dr. R. A. Reiss. 



Astronomical work is not largely represented, the onlv 

 exhibits we noticed being the spectrum of " Mars " in the 

 region of " a " compared with spectra of the moon, by 

 Mr. V. M. Slipher, which shows the presence of water 

 vapour in the atmosphere of the planet, and some lantern- 

 slides of the sun and sun-spots made by Mr. C. W. Barlow 

 using an old 4:j-inch refractor, with a deep vellow screen 

 interposed. C. J. 



KO. 2030, VOL. 78] 



THE BRITISH ASSOCIATION. 

 SECTION G. 



ENGINEERING. 



Opening Address by Dug.\ld Clerk, F.R.S., M.Inst.C.E., 



F.C.S., President of the Section. 

 At the middle of the last century the steam engine had 

 attained to a high degree of perfection. Its development 

 was, it is true, incomplete, but it had been successfully 

 applied to all the great duties of the mine, the water- 

 works, the factory, the railway, and the steamship. The 

 engines were mechanically excellent ; the fuel economy 

 was good, and they were built in units of thousands of 

 horse-power. Steam power, in fact, was revolutionising 

 the whole of the social and industrial conditions of the 

 globe. Notwithstanding this great material and engineer- 

 ing success, the world was in complete darkness as to the 

 connection between steam motive-power and heat. It was 

 seen that motive-power of almost any magnitude could 

 be obtained by the agency of heat ; but how it was obtained 

 and how much power was connected with a given quantity 

 of heat was quite unknown. The fuel consumptions of 

 existing engines were known, and certain modes of 

 improving economy were evident, and engineers were busily 

 engaged in testing these modes by the slow but sure 

 methods of invention, design, construction, and operation 

 in practical work ; but in this they had but little aid from 

 pure science. 



The science of thermodynamics did not yet exist. 



New light was dawning, however, which gradually 

 illumined the whole world of pure science and engineering 

 practice. 



Men of the first rank in intellect — Newton, Cavendish, 

 Rumford, Young, and Davy — had long before expressed 

 the opinion that heat was not material in its nature, but 

 was a mode of motion ; but their opinions, although to 

 some extent supported by experiment, made little 

 impression upon the scientific world, and in 1850 we still 

 find the most distinguished physicists adhering to the 

 " caloric " or material theory of heat. 



The great change, from the errors of the old theories 

 to the truth of the new, was due to the work of Joule, 

 Thomson, and Rankine in Great Britain, and of Carnot, 

 Meyer, Clausius, Helmholtz, and Hirn on the Continent. 

 The story begins with the work of Carnot in 1824, who 

 published in Paris in that year a pamphlet entitled " Re- 

 flections upon the Motive Power of Heat." He was 

 attracted by the problem of the steam engine and the air 

 engine. He saw that heat and motive power were con- 

 nected in some manner, and he endeavoured to settle in 

 a quantitative way the limits of that connection by the 

 invention of an ideal series of operations by means of 

 which the greatest conceivable amount of mechanical 

 power may be obtained from a given quantity of heat in 

 given circumstances. For the purpose of his demonstra- 

 tion he assumes only two things : (i) That if heat be 

 added to any body under standard conditions of tempera- 

 ture, pressure, and volume, and the body be carried 

 through any series of mechanical processes, returning 

 ultimately to the standard condition of temperature, 

 pressure, and volume, then the quantity of heat added to 

 the body is the same as that which has been discharged 

 from it ; (2) no process can exist whereby a given 

 mechanical energy can increase its own quantity. On 

 these indisputable assumptions he bases his ideal cycle, 

 which consists of four simple and easily imagined opera- 

 tions, occurring within a cylinder behind a piston, so 

 arranged that during the cycle work can be done by the 

 working fluid upon the piston or work done by the piston 

 on the working fluid. 



First Operation. — The given volume of the working 

 fluid is to be imagined as confined at its highest tempera- 

 ture and pressure behind the piston, and heat is to be 

 added to keep the temperature constant, while the fluid 

 expands, moving the piston and doing work upon it. 



Second Operation. — The supply of heat is cut off, and 

 the working fluid expands also during work on the piston, 

 while its temperature falls to the lowest point and its 

 volume increases to its maximum. 



